1. Field of the Invention
The invention relates to a device for controlling an internal combustion engine that operates with liquid and/or gaseous fuel.
2. Description of the Related Art
Typically, engines that operate with liquid and/or gaseous fuel are designed for high output, run at a predetermined constant speed, and drive a generator to generate electric current. The use of such engines is more preferably of interest where gaseous fuel as advantageous alternative to liquid fuel is easily available, such as for example in the case of stationary plants for power generation near gas extraction areas or for driving tankers transporting gas.
The necessity of being able to operate an engine with both gas and liquid fuel, such as diesel fuel, results from the fact that starting the engine is always only possible using liquid fuel, and that operation must be guaranteed even if the gas supply fails. Hence, it follows that it must be possible to change the engine over from one type of fuel to the other type of fuel during continuous operation.
A known type of fuel changeover in continuous operation provides for linearly throttling the supply of the fuel used up to then with a fixed predetermined rate starting from the current value at the start of the conversion as far as zero. The output of the rotational speed controller at the start of the conversion is separated from the fuel supply system of the fuel type up to now, reset to zero and connected to the fuel supply system of the new fuel type. Because of its normal manner of operation, the rotational speed controller subsequently increases the supply of the new type of fuel automatically to the correct extent in order to offset the increasing throttling of the supply of the previous fuel type until a stationary state in the exclusive operation with the new type of fuel is reached.
A disadvantage of this concept is that it only allows a gradual changeover and does not allow a rapid changeover from one fuel type to the other fuel type because the rotational speed controller is optimised for keeping the rotational speed constant and, therefore, can only offset slow throttling of the previous fuel type when no drop in power is allowed to occur. However, it is desirable to have the capability of a rapid changeover from operating the engine with gas to operating with liquid fuel because if the gas supply develops a leak, the gas supply must be interrupted immediately because of the explosion hazard.